This invention relates to the mounting of a compact circuit package to a heat sink or the like.
Heat conducting, electrically insulating substrates have been advantageously employed to retain heat generating electrical components along a first substrate side while a second oppositely disposed substrate side may be mounted to a heat sink to permit the heat generated by the electrical components to pass through the electrically insulating substrate to be dissipated at the external heat sink. One desirable construction is shown in U.S. Pat. No. 3,958,075.
A wide variety of circuit constructions may be located at or near the insulating substrate and within a cavity provided by the surrounding insulated housing. By way of example, see U.S. Pat. Nos. 4,196,411 and 4,218,724.
Referring more specifically to U.S. Pat. No. 4,218,724, heat conducting, electrically insulating substrates containing one or more heat generating electrical components have been advantageously connected to an insulating housing including a cavity surrounded by one or more edges or abutments which engage the substrate to limit the extent of entry of the substrate into the cavity. Clamping pressure may be applied to the insulating housing to clamp the substrate against an external heat dissipating object such as a heat sink to permit heat to pass from the substrate to the external heat sink without encountering any intervening thermal barriers such as solder, metalization, epoxy or the like.
The insulating housing is usually molded from a suitable plastic and provided with an upper cavity portion which is closed by the substrate and which contains the heat generating electrical components. The bottom housing portion is normally generally planular, surrounds the substrate, and is provided with relatively thin opposed outwardly extending mounting flanges through which threaded bolts or the like extend to mount the assembly to a heat sink.
The electrically insulating substrate, which is usually made from ceramic sheet material is mounted to the housing bottom surface and may be adapted to extend outwardly beyond the surface or may be flush therewith.
It is highly desirable to provide for maximum heat transfer between the ceramic substrate and the heat sink when the compact circuit package is mounted thereto. In order to fill the interstices in the substrate and heat sink surfaces, silicon grease has previously been manually applied to these surfaces before mounting to thereby improve the heat transfer characteristics. Such grease application was normally done in situ, wherein the circuit package installer dipped his fingers into a container of grease and spread the grease onto the ceramic substrate and heat sink with his fingers. This was not only messy, but also required that the installer had a supply of grease readily at hand.
It is an object of the invention to provide an improved concept of supplying and applying grease to the interface between the substrate of a compact circuit package and the heat sink to which the substrate is ultimately mounted.
In accordance with the various aspects of the invention, the bottom surface of the compact circuit package is provided with a self-contained chamber containing a supply of grease. The chamber is defined by the package bottom surface and a bubble of plastic film which overlies the substrate and which is removably sealed to the package around the periphery of the substrate. In this form, the compact circuit package can be transported and stored until ready for use.
When the package is ready to be mounted to a heat sink, pressure such as by a finger is applied to the top surface of the bubble film to thereby spreadingly apply the grease to the surface of the substrate. The film is then removed from the bottom of the compact circuit package and the greasy underside of the film placed into engagement with the heat sink surface and rubbed, as by a finger, to thereby spread the remaining residue grease onto the heat sink. The film is then removed and discarded and the compact circuit package mounted to the heat sink.
The present invention addresses and solves the need for a single, effective technique for providing thermoconductive material at the interface of the heat sink and the circuit package for enhancing heat transfer. Another solution is shown in my co-pending application Ser. No. 547,031, filed Oct. 31, 1983, now U.S. Pat. No. 4,546,410.